Method of preparing aluminum-magnesium alloys

ABSTRACT

Aluminum-magnesium alloys which contain from 50 to 98.6 percent by weight of aluminum may be prepared by adding oxide-free aluminum to a magnesium amalgam to form a binary amalgam which is then heated to a temperature sufficient to distill the mercury therefrom. This leaves as a distillation residue the alloys of the invention. The distillation is conducted under conditions of agitation and in the presence of an oxygen-free gas which is incapable of reacting with either aluminum, magnesium, mercury or combinations thereof. The aluminum-magnesium alloys produced by the process of the invention which contain from 50 to 70 percent by weight of aluminum are particularly useful in producing wellknown commercial aluminum alloys which contain 1.4 to 5 percent magnesium.

United States Patent [72] Inventor David G. Braithwaite Chicago, Ill. [21] Appl. No. 617 [22] Filed Jan. 5,1970 [45] Patented Oct. 26, 1971 [73] Assignee Nalco Chemical Company Chicago, Ill.

[54] METHOD OF PREPARING ALUMINUM- MAGNESIUM ALLOYS 10 Claims, 1 Drawing Fig.

[52] US. Cl 75/147, 75/67, 75/68, 75/81, 75/168, 75/169 [51] Int. Cl C22c 21/00 [50] Field of Search 75/147, 168,169,67,68, 81,135

[56] References Cited UNITED STATES PATENTS 2,926,990 3/1960 Cunningham et al 75/81 Primary Examiner-Richard 0. Dean Attorneys-Charles W. Connors, John G. Premo and Edward A. Ptacek ABSTRACT: Aluminum-magnesium alloys which contain from 50 to 98.6 percent by weight of aluminum may be prepared by adding oxide-free aluminum to a magnesium amalgam to form a binary amalgam which is then heated to a temperature sufficient to distill the mercury therefrom. This leaves as a distillation residue the alloys of the invention. The distillation is conducted under conditions of agitation and in the presence ofan oxygen-free gas which is incapable of reacting with either aluminum, magnesium, mercury or combinations thereof. The aluminum-magnesium alloys produced by the process of the invention which contain from 50 to 70 percent by weight of aluminum are particularly useful in producing well-known commercial aluminum alloys which contain 1.4 to 5 percent magnesium.

Na, AMALGAM SOLVENT SOLVENT-SHINE E CONDENSER 5 l6 SO 52 O -D- l2 7 BRINE cotqoenelam H CIELL ALU MINUM m STORAGE ans STORAGE METHOD OF PREPARING ALUMINUM-MAGNESIUM ALLOYS INTRODUCTION Magnesium amalgams are well known and have been of academic interest for many years. Magnesium amalgams have not been used commercially to any significant extent.

It is known that magnesium amalgams can be prepared by contacting aprotic solvent solutions of alkali metal amalgams with anhydrous magnesium salts, such as magnesium chloride, whereby an exchange reaction occurs and a magnesium amalgam is produced. Such a process is generally suggested in the teachings of U.S. Pat. No. 2,926,990.

It has been proposed to recover magnesium from magnesium amalgams by heating the amalgam to a temperature sufficient to allow the mercury to be distilled from the magnesium. This method of producing magnesium is not workable. It is now known that when attempts are made to remove mercury from magnesium amalgams not all of the mercury is disassociated from the amalgam. The reason for this phenomena is that magnesium is believed to form a mercuride which is a stable nonheat decomposable compound. If it were possible to process magnesium amalgams whereby they could be converted into useful products of commerce it would be of great industrial value.

One important use of magnesium is the combining of this metal with aluminum in amounts ranging from l.4 percent by weight to produce aluminum alloys having many utilitarian applications. These alloys are corrosion resistant in marine environments and possess excellent shaping and mechanical properties superior to pure aluminum. The invention contemplates processing magnesium amalgams by a series of process steps whereby these amalgams are converted to useful alloys of aluminum.

The invention further contemplates producing certain alloys of aluminum and magnesium which may be considered as metallurgical intermediates which may be used to produce a wide variety of specialized aluminum products.

OBJECTS OF THE INVENTION The invention provides the following:

I. A method of producing aluminum-magnesium alloys which contain from 5098.6 percent by weight of aluminum. i

2. A method of producing aluminum-magnesium alloys from magnesium amalgams.

3. A simplified method for recovering magnesium from its amalgams without substantial losses of mercury occurring.

4. An attractive method for producing aluminum-magnesium alloys which contain from 1.4-5 percent magnesium which alloys have a wide variety of industrial applications.

5. A combined process for easily converting magnesium chloride into valuable magnesium aluminum alloys.

TH E DRAWING For a better understanding of a preferred mode of the invention, reference may be had to the drawing which illustrates some of the more important features of the invention.

With specific reference to the drawing there is shown a conventional mercury cell which employs a mercury cathode and a graphite anode (not shown). Cells of this type are well known and are described in detail in Volume I, Encyclopedia of Chemical Technology, 2nd Edition.

The mercury cell 10 is supplied with sodium chloride brine through line 112, which is then electrolized under appropriate conditions to produce a sodium amalgam and chlorine gas which is removed from the cell through chlorine discharge line 14. Transfer line 16 removes produced amalgam from the mercury cell 10 and conveys it to a reactor 18. Also fed into reactor 18 through line 20 is an aprotic solvent for a magnesium salt. Line 22 feeds to reactor 18 a source of an anhydrous magnesium salt such as magnesium chloride. The sodium amalgam, solvent and magnesium chloride react to provide as a finished reaction product a dilute magnesium amalgam and a sodium chloride aprotic solvent brine which is removed from the reactor by means of line 24.

Dilute amalgam is transferred from reactor w by means of line 26 to an amalgam concentrator which is designated by the numeral 28. This concentrator contains a heat source shown in the drawing as heating coils 30 which allows the temperature of the dilute amalgam to be elevated to a point where the mercury vaporizes and is removed from the concentrator through line 32 where it is reliquified by means of an aircooled condenser 34 and is returned through line 36 to mercury cell 10.

Concentrated amalgam is withdrawn from amalgam concentrator 28 through line 37 into a reactor 38. This reactor is equipped with a heat source shown in the drawing as heating coils 40. Vertically positioned within the reactor is a screwtype agitator d2 which is powered by an electric motor 413. Also connected and in communication with the interior of reactor 38 is line 441 which feeds aluminum metal thereto. A similar line 46 feeds an inert oxygen-free gas to the reactor.

As the concentrated amalgam leaves amalgam concentrator 28 through line 37 and begins to fill reactor 38, gas is fed through line 46 into the reactor 38. During the filling of the reactor 38 with concentrated amalgam, or after it has been filled, aluminum metal is fed through line 44 to the reactor. During the addition of the aluminum, the gas, and the amalgam heat is continually applied to the reactor and the agitator 42 is in motion. The reactants are continuously agitated and the temperature is elevated to a point sufficient to vaporize the mercury which is removed as a vapor from the reactor through line 48 where it is liquified by air-cooled condenser 50 and returned through line 52 to mercury cell 10. After substantially all of the mercury has been removed from the reactor 38 there remains as a distillation residue an aluminummagnesium alloy which is removed from reactor 38 through line 54 to a suitable product storage container 56.

From the above description it is evident that the invention takes a magnesium salt and by a series of process steps converts it into a magnesium amalgam and then into a useful alloy of aluminum.

removed by distillation techniques at relatively moderate temperatures.

SPECIFICS OF THE INVENTION Amalgam Production In a preferred embodiment the invention contemplates utilizing as a starting material a magnesium amalgam which is produced by reacting aprotic solvent solutions of magnesium salts which for purposes of simplicity will be described as magnesium chloride with certain metal amalgams. These amalgarns are most suitably alkali metal amalgams with sodium amalgams providing a preferred type of starting alkali metal amalgam. Sodium amalgams of the type produced by the operation of a mercury cell are admirably suited for use.

It is important that the starting sodium amalgams be anhydrous which is readily accomplished by known means. The starting sodium amalgams of the types capable of production in a mercury cell may vary in sodium content between 0.1 up to about 3 percent by weight. More concentrated sodium amalgams may be used but their handling characteristics are such as to render them less suitable for large scale applications of the invention. Generally, the concentration of the sodium in the mercury will be between 0.1 to about 1 percent.

The Aprotic Solvents tetraethyleneglycol. Other glycol ether solvents that can be successfully employed may be defined by the general formula:

where R, and R, are the same or different hydrocarbon radicals, n is 2 to 6 and x is an integer, preferably 2 to 6. The oxyalkylene radicals represented by (C,,H,,,) are, for example,

Preferred diethers are those which are normally liquid at C.

To illustrate the glycol diethers more specifically, in the formula n can be 2 or 3 or both 2 and 3, x can be 3 or 4 and R, and R, can both be methyl or both ethyl, or both propyl, or both butyl, or both amyl, or both hexyl, or bothphenyl, or one can be ethyl and the other phenyl, or one can be ethyl and the other benzyl, or one can be ethyl and the other hexyl.

Conditions of the Reaction In its simplest embodiment the invention comprises contacting the aprotic solvent solution of magnesium chloride with sodium amalgams of the type described. The solvent solution and the amalgam are held in intimate contact or admixture for a period of time and at a temperature sufficient to produce a magnesium amalgam. As the magnesium amalgam is formed, the sodium of the starting amalgam is converted to a sodium chloride aprotic solvent brine. To illustrate this reaction reference may be had to the following equation:

In the case of producing magnesium from ether solutions of anhydrous magnesium chloride and sodium amalgams, it has been found that good results are obtained when the temperature of the reaction is at about l00 C. and the contact time ranges from l20 hours. At the end of the reaction, the magnesium has been transferred from its salt form into its amalgam form and the sodium originally present in the amalgam is in the form of sodium chloride which dissolved or suspended in the aprotic solvent.

While the reaction times have been set forth illustratively in relation to producing magnesium amalgams from alkali metal amalgams it will be understood that a wide range of reaction times and temperatures may be employed. A general rule that may be followed in most cases with respect to the temperature of the reaction is that such temperature should be below the boiling point of the particular aprotic solvent used. Beyond this no fixed reaction temperatures can be set forth generally since the temperature will vary depending upon such variables as the starting metal compound, the aprotic solvent, the concentration of the metal compound in the solvent, and the particular starting alloy with which the metal compounds are reacted. Routine experimentation may readily determine the optimum reaction conditions for each particular system sought to be used.

The aprotic solvent solution which contains dissolved or dispersed therein sodium chloride is removed from the amalgam. This solvent brine system may be then heated to recover the solvent by distillation. The residual sodium chloride may then be returned to the mercury cell for further reaction to convert it to additional sodium amalgam.

EXAMPLES To illustrate a typical method of producing magnesium from magnesium chloride and a sodium amalgam, the following is presented:

EXAMPLE I 1,000 grams of a 0.3 percent sodium amalgam were added to an 8-ounce bottle. To this amalgam was added dimethyl formamide which had dissolved therein 5 percent by weight of magnesium chloride to form a reaction mixture. The bottle was stoppered and placed in a glycol bath whose temperature was :5" C. The contents of the bottle were agitated by means of a magnetic stirring device. The agitation was continued for 30 minutes. At the end of this time an amalgam containing 0.12 percent by weight of magnesium was produced.

It is evident from the above-discussion of the methods for making the magnesium amalgam from the sodium amalgam that the concentration of the magnesium amalgam is in direct proportion to the amount of the sodium present in the starting sodium amalgam. Thus, the magnesium amalgams at this point in the process are extremely dilute. Most commonly they will contain at least 0.1 percent by weight but rarely will they contain more than 3 percent. It is to be understood that these amalgams may be. used to prepare the aluminum alloys more specifically described hereafter but from a practical standpoint it is beneficial that they be concentrated whereby their magnesium content is substantially increased.

Amalgam Concentration The dilute amalgams thus described, in a preferred embodiment of the invention, are subjected to a concentration step whereby the magnesium present in the mercury is increased to from about 10 to about 20 percent by weight. This concentration is achieved by heating the dilute amalgam to a temperature of at least 600 to as high as 800 C. to volatilize the mer- Formation of the Aluminum Alloys The concentrated amalgams are treated with from 50 to 98.6 percent, and preferably 50-70 percent, by weight of aluminum, based on the weight of the magnesium present in the alloy, to form a binary aluminum-magnesium amalgam. This amalgam, during its formation and during its subsequent processing, is treated with an oxygen-free gas which is incapable of reacting with either aluminum, magnesium or mercury or combinations thereof. After the formation of the aluminum-magnesium amalgam it is then heated to a temperature of at least 700 C. at which temperature the mercury vaporizes and is subsequently condensed and recovered for reuse in the process. The temperature at which the mercury volatilizes One of the more surprising features discovered in the development of the invention resides in the fact that the mercury is removed from the binary amalgam at relatively low temperatures. It was further found that for complete mercury removal from the amalgam to be achieved it is necessary that the binary amalgam be subjected to agitation in an amount sufficient to expose the entire surface of the amalgam to the particular heat source employed whereby the amalgam is uniformly and completely heated to the particular temperature used in the reaction.

Even in small laboratory runs with incomplete agitation it is possible to reduce the mercury content of the finished magnesium aluminum alloy so that it is less then 0.l percent by weight. in large scale equipment where good agitation and heat transfer are capable of being achieved it is possible to completely eliminate the mercury from the finished amalgam.

; The time required for removing the mercury from the binary amalgam varies depending upon the ratio of the ingredients, the temperature of the reaction and the degree and type of agitation used in the reactor. Laboratory experiments have indicated that good mercury removal may be accom plished in periods of time ranging from 4-14 hours.

These periods of times are based on the assumption that the binary amalgam is a reaction temperature of at least 700 C. When the concentrated magnesium amalgam is admixed with aluminum metal at room temperature and then heat applied to these reactants to elevate the temperature the reaction time, of necessity, is of much greater duration.

Two important discoveries made in the development of the invention and which contribute greatly to its success reside in the following facts:

A. The use of an inert gas during the formation of the alu minum-magnesium amalgam is essential, arid B. The starting aluminum metal must be substantially oxidefree.

The Inert Gases The inert gases must be incapable of reacting with any of the reactants used to produce the alloys, e.g., magnesium, aluminum or mercury. Thus it has been discovered that the noble gases, e.g., helium, neon, argon, krypton, xenon and radon, form a preferred group of inert gases with the most preferred gas being argon.

The Starting Aluminum Metal EXAMPLE ll One kilogram of a magnesium amalgam produced in accordance with example I was placed in a stainless steel autoclave which was fitted with an air-cooled condenser and was heated to a temperature of 650 C. for a period of 8 hours. During this heating mercury was vaporized, condensed and removed. At the end of this period of time the magnesium dissolved in the mercury had been concentrated to 20 percent by weight.

EXAMPLE Ill At the termination of the distillation shown in example II argon was fed to the reactor and a paddle stirrer was placed into the amalgam. At this point the temperature was slowly increased to 750 C., while at the same time aluminum chips were added to the reactor. The addition of the chips took about 20 minutes with the amount thereof being calculated, based on the weight of the magnesium present to provide 55 percent by weight of aluminum. Mercury was removed continuously throughout the heating period which was approximately 4 hours. The feed of argon was continued throughout this entire period. At the end of this time the agitator was withdrawn and the reaction mix allowed to cool. The finished product contained 54.88 aluminum, 45.0 magnesium and 0.12 mercury.

To illustrate how the 50-70 percent amalgams may be converted into aluminum amalgams containing from 1.4-5 percent by weight of magnesium, example IV is presented below.

EXAMPLE IV A binary alloy having the composition set forth in example Ill was added to molten aluminum in an amount to produce a 5 percent magnesium aluminum alloy.

in the preferred practice of the invention as described alloys containing from 50-70 percent by weight of aluminum are most conveniently prepared by following the steps described herein. These alloys are extremely useful in preparing from aluminum aluminum-magnesium alloys which contain from 1.4-5 percent by weight of magnesium. As mentioned before, alloys of this type are extremely valuable commercially and are used in many industrial applications.

I claim:

1. A method for preparing aluminum-magnesium alloys which contain from 50-98.6 percent by weight of aluminum which comprises the steps of:

A. Adding to a magnesium amalgam which contains at least 0.! percent by weight of magnesium, from 50-98.6 percent by weight, based on the weight of the magnesium present in said amalgam, of oxide-free aluminum to form a binary amalgam;

B. Distilling said binary amalgam at a temperature sufficient to reduce the mercury content thereof to below 0.15 percent by weight and recovering said mercury; and then,

C. Recovering as a distillation residue an aluminum-magnesium alloy which contains from 5098.6 percent by weight of aluminum with steps (A) and (B) being conducted under conditions of agitation and in the presence of an oxygen-free gas which is incapable of reacting with either aluminum, magnesium, or mercury or combinations thereof.

2. The method of claim l where in step (A) the magnesium amalgam contains from about 10-20 percent by weight of magnesium.

3. The method of claim 2 where the temperature of the magnesium amalgam is at least 600 C.

4. The method of claim 1 where the temperature used in step (B) is greater than 700 C.

5. The method of claim l where the oxygen-free gas is a noble gas.

6. The method of claim 5 where the noble gas is argon.

7. A method of preparing aluminum-magnesium alloys which contain from 50-70 percent by weight aluminum which comprises the steps of:

A. Adding to a liquid magnesium amalgam whose temperature is at least 600 C. and contains from about l0 percent to about 20 percent by weight of magnesium, from 50-70 percent by weight, based on the weight of the magnesium present in said amalgam, of oxide-free aluminum to form a binary amalgam;

B. Heating said binary amalgam to a temperature of at least 700 C. for a period of time sufficient to reduce the mercury content thereof to below 0. l5 percent by weight and recovering said mercury; and then,

C. Recovering as a distillation residue an aluminum-magnesium alloy which contains from 50-70 percent by weight aluminum with steps (A) and (B) being conducted under conditions of agitation and in the presence of a noble gas.

h. The method of claim 7 where the noble gas is argon.

9. A method of producing an aluminum alloy which conweight; tains from 1.4- percent of magnesium which comprises mix- C. Adding to the amalgam produced in step (B) from ing with aluminum the alloys produced in accordance with 50-98.6 percent by weight, based on the weight of the claim 7 in an amount sufficient to provide from 1.4-5 percent magnesium present in said amalgam, of oxide-free aluof magnesium in the finished alloy. 5 minum to form a binary amalgam;

10. A method of preparing aluminum-magnesium llo D. Heating said binary amalgam to a temperature of at least which contain from 50-98.6 percent by weight aluminum for a PMiod of mm Sumcicm to l'cduce the from magnesium chloride which comprises the steps of: Content thereof to below 0. p nt by ight and A. Contacting an alkali metal amalgam with an aprotic solrecovfling said y; and

vent l i of an anhydrous magnesium chloride f a 10 E. Recovering as a distillation residue an aluminum-magperiod of time and at a temperature sufficient to displace "esium which contains from Pcmem y alkali metal by magnesium from said amalgam, thereby weight aluminum f i a magnesium amalgam; with steps (C and (D) being conducted under conditions of B. Concentrating by evaporation the amalgam in step (A) to agtauon and m the Presence Ofa a magnesium concentration of from 10-20 percent by 

2. The method of claim 1 where in step (A) the magnesium amalgam contains from about 10-20 percent by weight of magnesium.
 3. The method of claim 2 where the temperature of the magnesium amalgam is at least 600* C.
 4. The method of claim 1 where the temperature used in step (B) is greater than 700* C.
 5. The method of claim 1 where the oxygen-free gas is a noble gas.
 6. The method of claim 5 where the noble gas is argon.
 7. A method of preparing aluminum-magnesium alloys which contain from 50-70 percent by weight aluminum which comprises the steps of: A. Adding to a liquid magnesium amalgam whose temperature is at least 600* C. and contains from about 10 percent to about 20 percent by weight of magnesium, from 50-70 percent by weight, based on the weight of the magnesium present in said amalgam, of oxide-free aluminum to form a binary amalgam; B. Heating said binary amalgam to a temperature of at least 700* C. for a period of time sufficient to reduce the mercury content thereof to below 0.15 percent by weight and recovering said mercury; and then, C. Recovering as a distillation residue an aluminum-magnesium alloy which contains from 50-70 percent by weight aluminum with steps (A) and (B) being conducted under conditions of agitation and in the presence of a noble gas.
 8. The method of claim 7 where the noble gas is argon.
 9. A method of producing an aluminum alloy which contains from 1.4-5 percent of magnesium which comprises mixing with aluminum the alloys produced in accordance with claim 7 in an amount sufficient to provide from 1.4-5 percent of magnesium in the finished alloy.
 10. A method of preparing aluminum-magnesium alloys which contain from 50-98.6 percent by weight aluminum from magnesium chloride which comprisEs the steps of: A. Contacting an alkali metal amalgam with an aprotic solvent solution of an anhydrous magnesium chloride for a period of time and at a temperature sufficient to displace alkali metal by magnesium from said amalgam, thereby forming a magnesium amalgam; B. Concentrating by evaporation the amalgam in step (A) to a magnesium concentration of from 10-20 percent by weight; C. Adding to the amalgam produced in step (B) from 50-98.6 percent by weight, based on the weight of the magnesium present in said amalgam, of oxide-free aluminum to form a binary amalgam; D. Heating said binary amalgam to a temperature of at least 700* C. for a period of time sufficient to reduce the mercury content thereof to below 0.15 percent by weight and recovering said mercury; and then, E. Recovering as a distillation residue an aluminum-magnesium alloy which contains from 50-98.6 percent by weight aluminum with steps (C) and (D) being conducted under conditions of agitation and in the presence of a noble gas. 